Acrylic acid or acrylate has a variety of industrial uses, typically consumed in the form of polymers. In turn, these polymers are commonly used in the manufacture of, among other things, adhesives, binders, coatings, paints, polishes, detergents, flocculants, dispersants, thixotropic agents, sequestrants, and superabsorbent polymers, which are used in disposable absorbent articles including diapers and hygienic products, for example. Acrylic acid is commonly made from petroleum sources. For example, acrylic acid has long been prepared by catalytic oxidation of propylene. These and other methods of making acrylic acid from petroleum sources are described in the Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 1, pgs. 342-369 (5th Ed., John Wiley & Sons, Inc., 2004). Petroleum-based acrylic acid contributes to greenhouse emissions due to its high petroleum derived carbon content. Furthermore, petroleum is a non-renewable material, as it takes hundreds of thousands of years to form naturally and only a short time to consume. As petrochemical resources become increasingly scarce, more expensive, and subject to regulations for CO2 emissions, there exists a growing need for bio-based acrylic acid or acrylate that can serve as an alternative to petroleum-based acrylic acid or acrylate. Many attempts have been made over the last 40 to 50 years to make bio-based acrylic acid or acrylate from non-petroleum sources, such as lactic acid (also known as 2-hydroxypropionic acid), 3-hydroxypropionic acid, glycerin, carbon monoxide and ethylene oxide, carbon dioxide and ethylene, and crotonic acid.
Petroleum-based superabsorbent polymer is made by polymerization of petroleum-based acrylic acid using methods described in Buchholz and Graham (eds), MODERN SUPERABSORENT POLYMER TECHNOLOGY, J. Wiley & Sons, 1998, pages 69 to 117, or recent patent applications, for example U.S. Patent Applications 2009/0275470 and 2011/0313113. The petroleum-based acrylic acid used in these methods is glacial acrylic acid with purity exceeding 98% and typically being 99.5% or higher. The typical major impurities in the petroleum-based glacial acrylic acid are propionic acid, acetic acid, maleic anhydride, maleic acid, acrolein, and furfural. On the other hand, the major impurities in the bio-based glacial acrylic acid, acrylic acid derivatives, or mixtures thereof produced from hydroxypropionic acid, hydroxypropionic acid derivatives, or mixtures thereof, are propionic acid, acetic acid, and hydroxypropionic acid, hydroxypropionic acid derivatives, or mixtures thereof.
Accordingly, there is a need for commercially viable processes of polymerizing bio-based glacial acrylic acid, acrylic acid derivatives, or mixtures thereof produced from the dehydration of hydroxypropionic acid, hydroxypropionic acid derivates, or mixtures thereof, to PAA for detergents, flocculants, and other applications; and SAP for use in diapers and other applications.